Gas wiping apparatus having adjustable gas guide

ABSTRACT

A gas wiping apparatus is a type of equipment for coating a molten metal onto a steel strip, in which the molten metal solution deposited on the steel strip is wiped to adjust a coating thickness. The gas wiping apparatus includes a body containing a high pressure gas and a multiple nozzle unit disposed at the body to eject the high pressure gas onto a surface of a moving coated steel strip. The surface of the coated steel strip passing through a hot dipping bath filled with the molten metal is wiped by a high speed gas jet. Here, the molten metal is prevented from splashing even at a high-speed and the steel strip can be adjusted in the coating thickness stably and uniformly.

TECHNICAL FIELD

The present invention relates to a gas wiping apparatus for coating amolten metal such as molten zinc on the surface of a steel strip, inwhich the molten metal solution deposited on the steel strip is wiped toadjust a coating thickness of the steel strip. More particularly, thepresent invention relates to a multi-nozzle gas wiping apparatus whichcan wipe the surface of the coated steel strip passing through a hotdipping bath filled with a molten metal by a high speed gas jet torestrain the molten metal from splashing even at a high-speed and adjusta coating thickness (coating thickness) of the coated steel strip stablyand uniformly.

BACKGROUND ART

A steel strip, especially a coated steel strip obtained by coating aspecific molten metal, e.g., molten zinc onto a cold-rolled steel strip,is highly corrosion-resistant and has aesthetic appearance.

Especially, lately, this coated steel strip has been utilized inelectronic products or automobiles, thus calling for development of amanufacturing method for a higher-quality coated steel strip.

The steel strip is chiefly coated by virtue of continuous hot dipgalvanizing.

For example, as shown in FIG. 1, a coil steel strip (cold-rolled steelstrip) S uncoiled from a pay off reel is thermally treated in a furnacethrough a welder and an entry looper. Then the coil steel strip S passesthrough a hot dipping bath 110 filled with molten zinc 112 through asnout 114 to be coated.

Next, the steel sheet passes through a gas wiping apparatus 120 (or anair knife) disposed over a molten level of the hot dipping bath. In thiscase, the molten metal solution (zinc) of the steel strip S isadequately worn from surfaces thereof by a high-pressure air or anon-active gas such as nitrogen, which will be hereinafter referred toas ‘gas’, blown onto the steel strip. This allows the steel strip to beadjusted in its coating thickness as shown in A of FIG. 1.

Afterwards, a gauge 130 measures whether the steel strip is coated to anappropriate coating thickness. The measured value is fed back to adjusta gas ejection pressure of the gas wiping apparatus 120 and an intervalbetween the steel strip S and the gas wiping apparatus 120, therebycontinuously controlling a coating amount of the steel strip.

Here, reference signs 116 and 118 in FIG. 1, which are not described,indicate a sink roll for guiding the steel strip into the hot dippingbath and a stabilizing roll for suppressing vibration of the steelstrip.

As described above, the gas wiping apparatus (air knife) 120 is theimportant equipment for determining a coating thickness of the steelstrip to meet consumer's demand.

FIG. 2 illustrates splashing of a molten metal solution (molten zinc)which occurs in a gas wiping apparatus 120.

As shown in FIG. 2, a high-speed high-pressure gas is ejected throughoutlets 122 e.g., slits formed between upper and lower lips of the gaswiping apparatus 120, to collide against surfaces of the steel strip.Here, molten metal particles, e.g., molten zinc particles, (which willbe hereinafter referred to as zinc chips) deposited on the steel stripare splashed due to gas moving upward and downward at a high speed.

For example, in FIG. 2, the gas ejected from the gas outlets at a highpressure and a high speed causes a negative pressure area to be formedaround the outlets owing to the gas traveling fast so that the zincchips d are splashed from the surfaces of the coated steel strip.

Meanwhile, currently, to boost production of the coated steel strip, thesteel strip is made to move at a higher speed. Also, to lower costs ofthe steel strip, a molten metal layer is required to be coated on thesteel strip to a thickness as small as possible within a desired extent.

In the case of thin coating, greater portions of the molten metal shouldbe worn from the surfaces of the coated steel strip passing through thehot dipping bath as indicated with reference numeral 110 of FIG. 1.Therefore, this requires gas to move at a higher speed, therebyincreasing a collision pressure.

However, as described above, the higher speed of the gas ejectedproportionally aggravates splashing of the zinc chips so that the gas islimitedly increased in its ejection speed.

The zinc chips d splashed as described above are deposited on or aroundthe outlets of the gas wiping apparatus, causing the gas to be ejectedwith non-uniform distribution along a width direction of the steelstrip. This results in defective coating of the steel strip.

Therefore, to restrain the molten metal from splashing during thincoating, currently the steel strip moves at a lower speed to be coated,thus limiting a high-speed travel of the steel strip and eventuallydegrading production of the steel strip.

Lately, a major concern with the gas wiping apparatus 120 is to ejectthe gas at a high speed and a high pressure while moving the steel stripfaster and maximally suppressing the zinc chips from splashing whichadversely affects product quality.

Conventionally, several technologies with regards to the gas wipingapparatus have been proposed to suppress the zinc chips from splashing.However, these technologies entail a complicated separate structureother than the gas wiping apparatus. Also, with the technologies, thezinc chips are not effectively prevented from splashing in an actualcoating process.

SUMMARY OF THE INVENTION

The present invention has been made to solve the foregoing problems ofthe prior art and therefore an aspect of the present invention is toprovide a multi-nozzle gas wiping apparatus, which can wipe the surfaceof a steel strip passing through a hot dipping bath filled with moltenmetal by a high speed gas jet while suppressing zinc chips from beingscattered even during a high-speed coating.

Another aspect of the invention is to provide a multi-nozzle gas wipingapparatus, in which multiple uniform pressure spaces (chambers) areformed to ensure a gas jet to be sprayed uniformly through the multiplenozzle unit along a width direction of a steel strip, and also turbulentcomponents of the gas jet are inhibited to allow the jet to be sprayedstably.

Technical Solution

According to an aspect of the invention, the gas wiping apparatusincludes a body containing a high pressure gas; and a multiple nozzleunit disposed at the body to eject the high pressure gas onto a surfaceof a moving coated steel strip.

Preferably, the body is configured as a chamber defining a space forcontaining the high pressure gas supplied through a gas feed pipe whichis connected to the body, and gas exhaust holes are perforated in a sidewall of the chamber, where the multiple nozzle unit is installed, tospray the high pressure gas therethrough.

More preferably, the body has a partition wall for dividing the spacefor containing the high pressure gas into first and second uniformpressure spaces, wherein the partition wall has gas passage holesperforated therein.

The multiple nozzle unit includes a main nozzle disposed at the sidewall of the chamber of the body to communicate with the gas exhaustholes in the chamber; and at least one auxiliary nozzle disposed overand under the main nozzle, respectively, to communicate with the gasexhaust holes.

Preferably, the main nozzle includes one nozzle, and the auxiliarynozzle includes first and second auxiliary nozzles disposed over andunder the main nozzle, respectively.

Also, the gas wiping apparatus further includes a third uniform pressurespace formed inside the main nozzle, communicating with the seconduniform pressure space of the chamber through the gas exhaust holes.

The main nozzle and the auxiliary nozzle include upper and lower lipsjoined to the side wall of the chamber, the upper and lower lipsdefining main and auxiliary gas outlets.

The main and auxiliary gas outlets are disposed at a predeterminedinterval sequentially from the chamber, in a moving direction of thesteel strip.

The chamber of the body includes a chamber body containing the highpressure gas therein; and a lip support unit disposed at the chamberbody and provided therein with the lips of the multiple nozzle unit.

The lip support unit includes lip supports having the upper and lowerlips of the main and the auxiliary nozzles slantingly and movablyengaged therewith; and a support body having gas exhaust orifices forexhausting the high pressure gas contained in the chamber toward the gasexhaust outlets formed between the lips, the support body integrallyconnected to the lip supports to support the wiping device against load.

The gas wiping apparatus further includes a first gas guide disposed inthe uniform pressure spaces of the chamber and configured to adjust anamount of the high-pressure gas flowing to the main and auxiliarynozzles.

The first gas guide includes guide plates which are rotatably connectedto a corresponding one of the lip supports for supporting the mainnozzle in the lip support unit, the guide plates installed rotatably inthe chamber by a driving unit vertically associated therewith.

The driving unit is disposed on the side wall of the chamber not tointerfere with a flow of the high-pressure gas and comprises a drivingcylinder having the guide plates connected thereto.

The gas wiping apparatus further includes a second gas guide disposed inthe uniform pressure spaces of the chamber and configured to allow thehigh-pressure gas to flow to the main nozzle and the auxiliary nozzle ata uniform amount.

The second gas guide comprises the guide plates which define a gaspassage opening in the second uniform pressure space while forming afourth uniform pressure space therebetween.

Advantageous Effects

In a multi-nozzle gas wiping apparatus according to the invention, thesurface of a steel strip passing through a hot dipping bath filled witha molten metal is wiped by a high speed gas jet. Meanwhile, zinc chipsare effectively prevented from splashing even during a high speedcoating, thereby increasing productivity of the coating process.

Moreover, multiple uniform pressure spaces (chambers) are formed insidethe gas wiping apparatus to ensure a gas jet to be sprayed uniformlythrough the multiple nozzle unit along a width direction of the steelsheet. Also, turbulent components of the jet are inhibited to ensure thejet to be sprayed stably.

Therefore, the gas wiping apparatus having the multiple nozzle unitprevents zinc chips from splashing by adjusting a coating thickness ofthe steel sheet. This also allows the gas to be ejected uniformly alonga width direction of the steel sheet, ultimately enhancing coatingquality of the steel strip.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a perspective view illustrating an example of a conventionalcontinuous hot dip galvanizing apparatus;

FIG. 2 is a view illustrating splashing of zinc chips in a conventionalgas wiping apparatus (air knife);

FIG. 3 is a schematic configuration view illustrating a multi-nozzle gaswiping apparatus according to the invention;

FIG. 4 is a view illustrating a gas wiping by the multi-nozzle gaswiping apparatus according to the invention;

FIG. 5 is a graph illustrating collision pressures of wiping gases on asteel strip in a conventional single nozzle apparatus and a multiplenozzle apparatus of the invention, respectively;

FIGS. 6( a) and (b) are graphs illustrating negative pressures generatedaround a corresponding nozzle in the conventional single nozzleapparatus and a multiple nozzle apparatus of the invention,respectively, in which FIG. 6( a) is a graph illustrating negativepressures generated at levels 10 cm up and down from the nozzle; and(FIG. 6( b) is a graph illustrating negative pressures generated atlevels 20 cm up and down from the nozzle;

FIG. 7 is a view illustrating operation of a three-nozzle gas wipingapparatus according to the invention;

FIG. 8 is a configuration view illustrating a multi-nozzle gas wipingapparatus according to a preferred embodiment of the invention;

FIG. 9 is an exploded perspective view of FIG. 8;

FIG. 10 is a configuration view illustrating a multi-nozzle gas wipingapparatus according to another embodiment of the invention;

FIG. 11 is a partial rear view of FIG. 10;

FIG. 12 is a partially broken perspective view of FIG. 10; and

FIG. 13 is a structural view illustrating a multi-nozzle gas wipingapparatus according to further another embodiment of the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will now be described in detail.

A gas wiping apparatus (or an air knife) adjusts a coating thickness ofa steel strip. In the gas wiping apparatus, a high-pressure gas (air orinactive gas) is blown at a high speed through a nozzle thereof tocollide against a steel strip, thereby generating a collision pressure.

Here, the higher pressure of the gas sprayed causes gas particles tomove more dynamically, thereby wiping a coating layer of the steel stripto a small thickness.

Also, as the steel strip travels faster, more gas should participate inwiping per unit time so that the gas should be ejected at a higherpressure or at a higher speed.

For example, when it comes to a gas wiping for adjusting a coatingthickness of the steel strip, the coating thickness is varied accordingto a moving speed of the steel strip, a pressure and speed of the gassprayed from the nozzle and a gap between the steel strip and thenozzle.

However, in a case where the steel strip needs to be coated thinly, thesteel strip can move faster by spraying the gas from the nozzle at ahigher pressure and accordingly increasing a collision pressure of thegas with respect to the steel strip.

Here, high-speed gas particles collide against the steel strip and areredirected to move along a length direction of the steel strip at a highspeed. The gas flowing along a length direction of the steel stripgenerates shear stress on surfaces of a molten metal deposited on thesteel strip. The gas will be hereinafter referred to as a ‘wall jet’.

Therefore, when such shear stress surpasses surface tension of a moltencoating layer of the steel strip, particles of the molten coated layerfall off, causing metal chips or zinc chips to be splashed as shown inFIG. 2.

Meanwhile, in the conventional gas wiping apparatus using a singlenozzle shown in FIG. 2, for example, the zinc chips are splashed, whenthe steel strip travels at a speed of 160 mpm and is coated to a coatingthickness up to 40 g/m².

Therefore, when the steel strip moves at a speed of at least 160 mpm, inthe conventional gas wiping apparatus (air knife), the steel strip ishardly coated to a coating thickness of up to 40 g/m².

That is, with a rapidly rising demand for the coated steel strip for usein, e.g., automobiles or electric products, high-speed coating or thincoating has faced a limitation.

Therefore, the gas wiping apparatus of this invention ensures the steelstrip to be coated to a small thickness even at a high speed.

Exemplary embodiments of the present invention will now be described indetail with reference to the accompanying drawings.

First, FIG. 3 illustrates basic configuration of a multi-nozzle gaswiping apparatus 1.

As shown in FIG. 3, the gas wiping apparatus 1 having the multiplenozzle unit includes a body 10 for containing a high-pressure gas (airor inactive gas) and a multiple nozzle unit 30 installed at the body toeject the high-pressure gas onto a moving, coated steel strip.

Here, the body 10 is configured as a chamber defining a space 20 forcontaining the high-pressure gas therein. Such a chamber is joined to aframe which fixes the apparatus to both sides of the moving steel strip.

Also, gas exhaust holes 12 a are perforated in a side wall 12 of thechamber, where the multiple nozzle unit 30 is installed, to spray thehigh pressure gas therethrough.

Moreover, the body 10 has a horizontal partition wall 14 for dividingthe space 20 into first and second uniform pressure spaces 20 a and 20b. The partition wall 14 has gas passage holes perforated therein.

Preferably, as will be explained in detail below, the body 10 furtherincludes a third uniform pressure space 20 c formed inside a main nozzle32, communicating with the second uniform pressure space 20 b of thechamber through the gas exhaust holes 12 a.

Therefore, referring to FIG. 3, the gas is provided at a high pressurethrough a high pressure feed pipe 18 which is connected to a side wall(16 of FIG. 9) of the chamber 10 or to an upper part thereof. When thegas is fed through the high pressure feed pipe 18 connected, the gas isfed to the second uniform pressure space 20 b from the first uniformpressure space 20 a through the gas passage holes 14 a. Subsequently,the gas is exhausted to the third uniform pressure space 20 c disposedinside the main nozzle 32 through the gas exhaust holes 12 a perforatedin the side wall of the chamber.

In this fashion, the high-pressure gas is distributed uniformly to eachof the uniform pressure spaces and then sprayed through the main nozzle32 and first and second auxiliary nozzles 34 and 36 of the multiplenozzle unit 30.

That is, the high-pressure gas is ejected uniformly along a widthdirection of the steel strip through the main nozzle 32 and the firstand second auxiliary nozzles 34 and 36, thus allowing the steel strip tobe coated with a uniform thickness.

As shown in FIG. 3, the multiple nozzle unit 30 is disposed at the sidewall of the chamber to communicate with the gas exhaust holes 12 aperforated in the side wall 12 of the chamber 10. Also, the multiplenozzle unit 30 includes the main nozzle 32 for adjusting a coatingthickness of the steel strip and the first and second auxiliary nozzles34 and 36 disposed over and under the main nozzle 32 to connect to thegas exhaust holes. Here, the auxiliary nozzles 34 and 36 serve toprevent the molten metal from splashing.

That is, according to characteristics of the invention, the gas wipingapparatus 1 includes the main nozzle 32 and at least one auxiliarynozzle, preferably, the first and second auxiliary nozzles 34 and 36sequentially disposed over and under the main nozzle 32.

Reference signs 32 c, 34 c and 36 c in FIG. 3, which are not described,denote gas exhaust outlets of the nozzles.

FIG. 4 illustrates gas colliding against a steel strip when sprayedthrough a multiple nozzle unit 30 including a main nozzle 32 and atleast one auxiliary nozzle (first auxiliary nozzle) 34.

That is, as shown in FIG. 4, a main gas G1 sprayed from the main nozzle32 collides against surfaces of the steel strip S to adjust a coatingthickness thereof. A gas G2 sprayed from the first auxiliary nozzle 34surrounds the main gas G1, thereby preventing zinc chips (metal chips)from splashing as described with reference to FIG. 2.

For example, the gas sprayed from the main nozzle may have greater shearstress along a length direction of the steel strip than surface tensionof a coating layer. However, in this case, the gas ejected from thefirst auxiliary nozzle surrounds the main gas from the main nozzle,thereby preventing zinc chips from splashing caused by the gas ejectedfrom the main nozzle.

Then, FIG. 5 illustrates a collision pressure of gas with respect to asteel strip in a case where a conventional single nozzle is employed,and main and auxiliary nozzles are adopted together, respectively.

That is, as shown in FIG. 5, in a case where the auxiliary nozzle isemployed, the collision pressure of the gas with respect to the steelstrip in a moving direction of the steel strip is higher than in a casewhere only the single nozzle (indicated with ‘no auxiliary nozzle’) isemployed.

That is, according to the invention, the gas ejected from the mainnozzle and the gas ejected from the auxiliary nozzle cooperativelyincrease a collision pressure of the entire gas with respect to thesteel strip. At the same time, the gas ejected from the auxiliary nozzleprevents zinc chips from splashing.

Therefore, when a coating amount is adjusted with the gas ejected at anidentical speed in the conventional single nozzle and the main andauxiliary nozzles, respectively, the collision pressure of the sprayedgas with respect to the steel strip is increased in the gas wipingapparatus 1 of the invention, assuring the steel strip to be coatedthinly while suppressing zinc chips from splashing.

FIGS. 6 a and 6 b illustrate negative pressures generated at levels 10cm and 20 cm from the center of the nozzle with respect to a movingdirection of a steel strip.

That is, as shown in FIG. 6 b, in a case where the main nozzle 32 andthe auxiliary nozzles 34 are employed, the wall jet is insufficientlydecreased in its speed. This generates a negative pressure resultingfrom the high speed flow of gas in areas a bit away from a collisionpoint along a length direction of the steel strip, i.e., 20 cm up anddown from the center of the nozzles. This potentially causes the zincchips to splash.

However, as shown in FIG. 6 a, a negative pressure due to the high-speedflow of gas hardly occurs in areas less away from the collision pointalong a length direction of the steel strip, i.e., 10 cm up and downfrom the center of the nozzle.

Accordingly, as shown in FIG. 3, preferably, the second auxiliary nozzle36 is installed together with the first auxiliary nozzle 34. Thisincreases an ambient pressure and eliminates a negative pressurepartially generated on the steel strip around the nozzles of the gaswiping apparatus (air knife), thereby forming an activated positivepressure. This prevents zinc chips from splashing on the entire moltencoating layer of the steel strip.

FIG. 7 illustrates distribution of gas sprayed in a most desirable casewhere a main nozzle 32 and first and second auxiliary nozzles 34 and 36are employed in a multi-nozzle gas wiping apparatus 1.

The main nozzle 32 and the first auxiliary nozzle 34 of the multiplenozzle unit 30 eject gases G1 and G2 necessary for gas wiping whichmeets high-speed thin coating conditions.

The second auxiliary nozzle 36 ejects a gas G3 at a relatively lowerspeed than the main nozzle and the first auxiliary nozzle. Thus, gasparticles sprayed from the main nozzle at a high speed, collide againstthe steel strip, and are mixed with gas particles ejected from at leastthe second auxiliary nozzle (preferably first and second auxiliarynozzles) at a lower speed to decrease the overall gas speed. Thisaccordingly allows the wall jet to move at a lower speed along a lengthdirection of the steel strip. This weakens shear stress and thusrestrains zinc chips from splashing.

FIGS. 8 to 13 illustrate detailed structures of a multi-nozzle gaswiping apparatus 1 of the invention, whose basic functions have beenexplained above.

First, FIGS. 8 and 9 illustrate a gas wiping apparatus 1 including a lipsupport unit 24 according to another embodiment of the invention of FIG.3.

For example, the body 10 of the invention described above is configuredas a chamber, and includes a space 20 for containing a high-press gascomposed of first to third uniform pressure spaces 20 a, 20 b and 20 c,a chamber body 22 fixed to the fixing frame and a lip support unit 24provided to the chamber body and having a main nozzle and first andsecond auxiliary nozzles.

Here, the lip support unit 24 includes lip supports 26 and a supportbody 28. The lip supports 26 have upper and lower lips of the main,first and second nozzles 32, 34 and 36 slantingly and movably engagedtherewith. The support body 28 has gas exhaust orifices 28 a forexhausting the high-pressure gas toward gas exhaust outlets and isintegrally connected to the lip supports to support the wiping deviceagainst load.

Therefore, in the gas wiping apparatus 1 according to the modifiedembodiment of the invention as shown in FIGS. 8 and 9, the lip supportunit 24 constitutes a main body to sustain load. Accordingly, to renderthe chamber body 22 of the invention sufficiently strong, a thickness ofthe chamber body 22 engagingly fixed to the lip support unit 24 does notneed to exceed that of a chamber body of a conventional gas wipingapparatus.

Here, to build the chamber body 22, flanges f with three bent pieces 22a, 22 b, and 22 c are assembled together by bolts and nuts to enableseparate components to be installed therein in a case where the gaswiping apparatus undergoes maintenance and repair, or is fabricated. Theupper and lower pieces 22 a and 22 c of the chamber are connected to theupper and lower lip supports 26 of the lip support unit, respectively.

Meanwhile, the main nozzle 32 and the first and second auxiliary nozzles34 and 36 include the main lip 32 a and 32 b and the first and secondupper and lower lips 34 a, 34 b; 36 a, 36 b which can be assembled anddissembled on the lip supports 26 of the lip support unit 24. Thesemain, first and second upper and lower lips are slantingly installed onslanted surfaces of the lip supports 26.

Here, the lips have slits h perforated therein to bolt the lipstherethrough on the slanted surfaces of the lip supports 26. This allowsthe lips to be adjustably positioned.

As a result, as shown in FIGS. 8 and 9, in the gas wiping apparatus 1 ofthe invention, a main outlet 32 c is formed at a distal end of thecentral main lips 32 a and 32 b. First auxiliary outlets 34 c are formedbetween the main lips and the first upper and lower auxiliary lips 34 aand 34 b. Likewise, second auxiliary outlets 36 c are formed between thefirst auxiliary upper and lower lips 34 a and 34 b and the second upperand lower auxiliary lips 34 a, 34 b, 36 a and 36 b, respectively.

What is important, the main outlet 32 c is located most adjacent to thesteel strip and then the first and second auxiliary outlets 34 c and 36c of the first and second auxiliary nozzles are located next to the mainoutlet 32 c sequentially.

Therefore, when gases are ejected at an identical speed, the gas ejectedfrom the main outlet exhibits a greatest collision pressure with respectto the steel strip, followed by the first and second auxiliary nozzles.When it comes to the speed of the gas sprayed onto the steel strip, thegas is most slowly ejected from the second auxiliary outlet which islocated at a greatest distance.

That is, as shown in FIG. 7, the gas ejected from the main outlet andthe first auxiliary outlets adjusts a coating thickness of the steelstrip. Meanwhile, the gas ejected from the first and second auxiliaryoutlets decreases the wall jet, thereby restraining zinc chips fromsplashing.

Here, reference numeral 16 of FIG. 9 denotes a side wall of the body(chamber) 10.

FIGS. 10 to 12 illustrate gas wiping apparatuses 1 according to otherembodiments of the invention.

As shown in FIG. 10, the gas wiping apparatus according to the modifiedembodiment of the invention further includes a first gas guide 50disposed in the second uniform pressure space of the chamber andconfigured to adjust an amount of a high-pressure gas flowing to mainand auxiliary nozzles.

The first gas guide 50 includes guide plates 50 a and 50 b which arerotatably connected to a corresponding one of lip supports 26 forsupporting the main nozzle 32. The guide plates 50 a and 50 b areinstalled rotatably in the second uniform pressure space by a drivingunit 52 or a driving cylinder vertically associated therewith.

Therefore, the guide plates 50 a and 50 b are pivoted about a lipsupport unit by the driving cylinder 52. This adjusts the amount of aninternal gas flowing to the first and second auxiliary nozzles 34 and36.

Meanwhile, the driving unit 52 or the drive cylinder, as shown in FIGS.11 and 12, is disposed vertically in a protrusion 16 a formed on a sidewall 16 of the body (chamber) 10 and inside a cover 51 not to interferewith a flow of the high-pressure gas. Also, the driving cylinder 52 hasthe guide plates connected thereto.

Consequently, with the driving cylinder operated, the guide plates 50 aand 50 b are rotated about a hinge point of the lip support unit toadjust an amount of the gas flowing to the first and second auxiliarynozzles 34 and 36.

Here, although not designated with reference numerals in the drawings,rods of the driving cylinder are connected to the guide plates,respectively, in a structure having slits and hinge pins which can movein response to the rotation of the guide plates.

Meanwhile, in a case where the driving cylinder 52 is moved by thestroke of the rods that operate identically, the upper and lower guideplates are rotated at an identical amount. On the other hand, in a casewhere the driving cylinder 52 is driven separately, the upper and lowerguide plates can be separately adjusted in their rotational amount.

FIG. 13 illustrates a gas wiping apparatus 1 according to furtheranother embodiment of the invention.

The gas wiping apparatus according to this modified embodiment of theinvention further includes a second gas guide 54, i.e., guide platesdisposed in a second uniform pressure space of the chamber andconfigured to allow a high-speed gas to flow to main and auxiliarynozzles at a uniform amount.

In consequence, the second guide plates 54 define a gas passage openingin the second uniform pressure space while forming a fourth uniformpressure space 20 d therebetween. This ensures the gas to be ejectedfrom the main nozzle and the first and second auxiliary nozzles withuniform distribution even despite a change in the flow rate or pressureof the gas.

INDUSTRIAL APPLICABILITY

As set forth above, according exemplary embodiments of the invention, amulti-nozzle gas wiping apparatus can wipe the surface of a steel strippassing through a hot dipping bath filled with molten metal by ahigh-speed gas jet. Moreover, the molten metal is inhibited fromsplashing even during a high-speed coating, and eventually, a coatingthickness (coating amount) of the steel strip can be adjusted stably anduniformly.

While the present invention has been shown and described in connectionwith the preferred embodiments, it will be apparent to those skilled inthe art that modifications and variations can be made without departingfrom the spirit and scope of the invention as defined by the appendedclaims.

The invention claimed is:
 1. A gas wiping apparatus comprising: a bodyincluding a chamber defining a space for containing a high pressure gas;a multiple nozzle unit disposed at the body to eject the high pressuregas onto a surface of a moving coated steel strip, wherein the multiplenozzle unit comprises a main nozzle disposed at the chamber and at leastone auxiliary nozzle disposed over or under the main nozzle; and a firstgas guide disposed in the chamber and configured to adjust an amount ofthe high-pressure as flowing to the main and auxiliary nozzles, whereinthe first gas guide comprises guide plates installed in the chamber androtatably driven by a vertically disposed driving unit therewith,wherein the driving unit is disposed on a side wall of the chamber notto interfere with a flow of the high-pressure gas and comprises adriving cylinder having the guideplat connected thereto.
 2. The gaswiping apparatus according to claim 1, wherein the high pressure gas issupplied through a gas feed pipe which is connected to the body; andwherein gas exhaust holes are perforated in a side wall of the chamber,where the multiple nozzle unit is installed, to spray the high pressuregas therethrough.
 3. The gas wiping apparatus according to claim 1,wherein the body has a partition wall for dividing the space forcontaining the high pressure gas into first and second uniform pressurespaces, wherein the partition wall has gas passage holes perforatedtherein.
 4. The gas wiping apparatus according to claim 1, wherein themain nozzle is disposed at the side wall of the chamber to communicatewith the gas exhaust holes in the chamber; and wherein the auxiliarynozzle is disposed over or under the main nozzle, respectively, tocommunicate with the gas exhaust holes.
 5. The gas wiping apparatusaccording to claim 4, wherein the main nozzle comprises one nozzle, andthe auxiliary nozzle comprises first and second auxiliary nozzlesdisposed over and under the main nozzle, respectively.
 6. The gas wipingapparatus according to claim 3, further comprising a third uniformpressure space formed inside the main nozzle, communicating with thesecond uniform pressure space of the chamber through the gas exhaustholes.
 7. The gas wiping apparatus according to claim 4, wherein themain nozzle and the auxiliary nozzle comprise upper and lower lipsjoined to the side wall of the chamber, the upper and lower lipsdefining main and auxiliary gas outlets.
 8. The gas wiping apparatusaccording to claim 7, wherein the main and auxiliary gas outlets aresequentially disposed at predetermined intervals from the chamber, in amoving direction of the steel strip.
 9. The gas wiping apparatusaccording to claim 7, wherein the chamber comprises: a chamber bodycontaining the high pressure gas therein; and a lip support unitdisposed at the chamber body and provided therein with the lips of themultiple nozzle unit.
 10. The gas wiping apparatus according to claim 9,wherein the lip support unit comprises: lip supports having the upperand lower lips of the main and the auxiliary nozzles slantingly andmovably engaged therewith; and a support body having gas exhaustorifices for exhausting the high pressure gas contained in the chambertoward the gas exhaust outlets formed between the lips, the support bodyintegrally connected to the lip supports to support the wiping deviceagainst load.
 11. The gas wiping apparatus according to claim 9, whereinthe first gas guide is disposed in the uniform pressure spaces of thechamber.
 12. The gas wiping apparatus according to claim 11, wherein theguide plates of the first gas guide are rotatably connected to acorresponding one of the lip supports for supporting the main nozzle inthe lip support unit.
 13. The gas wiping apparatus according to claim 3,further comprising a second gas guide disposed in the uniform pressurespaces of the chamber and configured to allow the high-pressure gas toflow to the main nozzle and the auxiliary nozzle at a uniform amount.14. The gas wiping apparatus according to claim 13, wherein the secondgas guide comprises the guide plates which define a gas passage openingin the second uniform pressure space while forming a fourth uniformpressure space therebetween.